Here is what is likely to damage the different types of charge controllers.
Excessive voltage can damage both MPPT and PWM charge controllers. But MPPT charge controllers deal with higher voltages than PWM charge controllers. It’s because PWM charge controllers will lower the voltage without increasing the current. So people will only connect it to solar panels of the same nominal voltage.
An MPPT charge controller will increase the current when it lowers the voltage. So it allows higher voltage inputs for greater efficiency. This efficiency means that people will subject it to higher voltages. Also, solar panels produce higher voltages in colder temperatures. So, MPPT charge controllers are more likely to get damaged high voltages.
An MPPT charge controller can limit the current, but a PWM charge controller cannot. Also, a PWM charge controller is more likely to receive a high current input than an MPPT charge controller. Also, a phenomenon called cloud edge effect can increase the current. It happens when sunlight reflected off a cloud’s edge adds to the sunlight reaching the solar panels. This all means that a PWM charge controller is more likely to get damaged by a high current.
Here is how to protect a PWM charge controller.
Multiply the short circuit current of the solar panels by the number of panels (or strings) connected in parallel. Take the result and multiply by 1.25 to allow for cloud edge effect. Choose a charge controller with an amperage rating greater than this. If you cannot find a charge controller to handle this, you can use 2 or more charge controllers in parallel.
Here is an example:
Number of panels in parallel: 5
Solar panel nominal voltage: 12 volts
Solar panel maximum short circuit current: 8.86 amps
Here is the calculation:
8.86 amps x 5 x 1.25 = 55.375 amps
So, you will need a charge controller that can handle over 55.375 amps. In fact, you can use a charge controller that is rated for over 60 amps and protect it with a 60 Amp DC circuit breaker.
Here is how to protect an MPPT charge controller.
Multiply the open circuit voltage of the solar panels by the number of panels in series. Multiply this result by the ambient temperature correction factor. Choose a charge controller that can handle this voltage.
Here is an example:
Number of solar panels in series: 5
Solar panel open circuit voltage: 22.32 volts
The coldest ambient air temperature that is probable: -6 degrees Fahrenheit
Ambient temperature correction factor based on -6 degrees Fahrenheit: 1.20 (see chart below)
Here is the calculation:
22.32 volts x 5 x 1.20 = 133.92 volts
So, you will need a charge controller that can handle over 133.92 volts.
| Voltage Correction Chart | ||
| Temperature in degrees Celsius | Temperature in degrees Fahrenheit | Temperature Correction Factor |
| 24 to 20 | 76 to 68 | 1.02 |
| 19 to 15 | 67 to 59 | 1.04 |
| 14 to 10 | 58 to 50 | 1.06 |
| 9 to 5 | 49 to 41 | 1.08 |
| 4 to 0 | 40 to 32 | 1.10 |
| -1 to -5 | 31 to 23 | 1.12 |
| -6 to -10 | 22 to 14 | 1.14 |
| -11 to -15 | 13 to 5 | 1.16 |
| -16 to -20 | 4 to -4 | 1.18 |
| -21 to -25 | -5 to -13 | 1.20 |
| -26 to -30 | -14 to -22 | 1.21 |
| -31 to -35 | -23 to -31 | 1.23 |
| -36 to -40 | -32 to -40 | 1.25 |
In summary, pulse width modulated (PWM) charge controllers work best with low voltage, high current outputs from solar arrays. So, PWM charge controllers are more likely to face damage from high current (amperage). You protect it by making sure it can handle more than the output current from the solar array (adjusted for cloud edge effect). You can also use two or more charge controllers in parallel if the current is too much for just one. A circuit breaker can also help. A Maximum Power Point Tracking (MPPT) charge controller works better with high voltage from the solar array. So you will need high voltage protection. Make sure that the MPPT charge controller can handle a higher voltage than the solar panel output. You should also adjust for cold temperatures. These measures will make sure that you have a safe and reliable solar power system.